/ 1 4- 


U.  S.  DEPARTMENT  OF  AGRICULTURE, 

BUREAU  OF  ENTOMOLOGY     CIRCULAR  No.  164. 

L.  O.  HOWARD.  Entomologist  *nd  Chief  oi  Bureau. 


THE  GIPSY  MOTH  AS  A  FOREST  INSECT. 

WITH  M  SeESTIOHS  kS  TO  lis  CONTEOL. 


BY 


W.    F.    FISKE, 


673W-13 1 


WA4HINCTON  :  GOVERNMENT  WIINTINO  OFFKE  :  1(11 


BUREA  U  OF  EKTOMDWa  Y. 

L.  0.  Howard,  Entomologist  and  Chief  of  Bureau. 
C.  L.  Marlatt,  Entomologist  and  Acting  Chief  in  Absence  of  Chief. 
R.  S.  Clifton,  Executive  Assistant. 
W.  F.  Tastet,  Chief  Cleric. 
F.  II.  Chittenden,  in  charge  of  truck  crop  and  stored  product  insect  investigations. 
A.  I).  Hopkins,  in  charge  of  forest  insect  investigations. 
W.  I).  Hunter,  in  charge  of  Southern  field  crop  insect  investigations. 
F.  M.  Webster,  in  charge  of  cereal  and  forage  insect  investigations. 
A.  L.  Quaintance,  in  charge  of  deciduous  fruit  insect  investigations. 
E.  V.  Phillips  in  charge  of  ha  culture. 
Rolla  P.  Currie,  in  charge  of  editorial  work. 
Mabel  Colcord,  in  charge  of  library. 

Preventing  Spread  of  Moths. 

laboratory. 

(At  Melrose  Highlands,  Mass.) 

A.  F.  Burgess,  in  charge  of  biological  i /instigations: 

W.  F.  Fiske,  in  charge  of  parasite  and  disease  investigations. 

Kenneth  W.  Brown,  C.  W.  Collins,  J.  J.  Culver,  John  E.  Dudley,  Jr., 
Hartley  R.  Gooch,  Chas.  W.  Minott,  F.  H.  Mosher,  Harold  A.  Preston, 
E.  A.  Proctor,  John  V.  Schaffner,  Jr.,  M.  B.  Shepherd,  C.  W.  Stock  well, 
J.  N.  Summers,  W.  B.  Turner,  Reginald  Wooldridge,  assistants. 

field  work. 

D.  M.  Rogers,  in  charge  of  Eastern  territory. 
L.  II.  Worthley,  in  charge  of  Western  territory. 

Harold  A.  Ames,  I.  L.  Bailey,  Henry  X.  Bean.  Frank  W.  Graves,  Jr.,  II.  L. 
McIntyre,  D.  G.  Murphy,  Charles  E.  Totman,  H.  W.  Vinton,  assistants. 
ii 


Circular  No.  164 

I  nited  States  Department  of  Agriculture, 

BUREAU  OK   ENTOMOLOGY. 
L.  O.  HOWARD,   Entomologist  and  Chief  of  Bureau. 


Till    QIPST  MMTII   AS    v  FOHKsl    INSECT,    WITH    SUGGESTIONS    kS 

TO  ITS  CONTROL 

By  W.  I'.  FisKi 
Agi 

mi     OIFST-MOTB    Mil   \ii<>\.    PAST    \\i>   PRESENT. 

It  has  been  said  of  the  gipsy  moth  thai  the  caterpillar  is  almosl 
omnivorous  so  far  as  foliage  is  concerned,  and  the  earrj  reports  ] >u I >- 
lished  by  the  State  Board  <>l'  Agriculture  of  Massachusetts  abound  in 
references  confirmatory  of  this  statement.  It  is  in  facl  incontro- 
\  ertible,  from  the  ma—  of  evidence  furnished  by  these  reports  as  well 
as  by  the  contemporaneous  accounts  in  the  press,  thai  thegipsj  moth 
was  formerly  almosl  unique  amongst  injurious  insects  in  its  ability 
to  destroy  all  sorts  of  vegetation.  Upon  the  occasion  of  it-  historic 
outbreak  in  Medford  and  Maiden,  beginning  about  1889,  mid  again  in 
the  larger  outbreak  following  a  few  years  after  the  extermination 
work  was  concluded  in  1900,  not  only  forest,  -hade,  and  ornamental 

t  fees  hut  Orchards,  gardens,  and  Held-  were  defoliated  and  deva-t  at  ed. 

Ami  when  the  food  supplj  was  exhausted  the  starving  caterpillars,  by 
force  of  numbers  alone,  constituted  a  veritable  plague,  rendering  the 
streets  almost  impassable  to  pedestrians,  massing  upon  and  entering 
houses,  and  infesting  the  bedrooms,  the  kitchen-,  and  even  the  dining 
tables  as  well  as  all  outdoors. 

It  i-  needless  to  state  that  these  conditions  no  longerprevail.  ( later- 
pillars  there  are,  during  their  season  ;  egg  masses  in  varying  abundance 
are  everywhere  to  be  found  in  neglected  woodland-,  and  thousands 
of  dead  and  dying  tree-  -tand  as  evidence  that  unless  it  he  rendered 
-till  further  innocuous  the  gipsy  moth  i-  -till  a  very  living  factor  to  be 
considered  in  the  future  of  American  forestry.  Bui  the  accounts  of 
its  earlier  depredations  seem  all  hut  incredible  when  compared  with 
condition-  to-dav.      It  i-  no  longer  prominent  as  a  field  and  garden  pesl 

nstderattao  <  noth  (Porthr/ria  dhpar  I  It"  disease, 

natural  raa  ol  trees  to  attack  by  th<?  gipsy  moth,  as  applied  bribe  manajrenv 

knots. 

1 


2  THE   GIPSY    MOTH    AS  A   FOREST   INSECT. 

As  an  orchard  insect  it  is  not  infrequently  eclipsed  by  the  American 
tent  caterpillar.  Even  the  forests  have  suffered  less  than  early  pre- 
dictions would  have  led  one  to  expect.  It  is  certain  that  the  situation 
has  become  measurably  improved  within  recent  ""ears. 

CAUSES    OF    THE    IMPROVED   CONDITIONS. 

This  obvious  improvement  is  in  part  only  apparent  and  in  part 
very  real  and  due  to  a  variety  of  causes.  The  apparent  amelioration 
is  due  to  the  fact  that  the  gipsy  moth  is  at  present  most  active  in  a 
,  belt  of  towns  beyond  the  limits  of  the  densely  populated  metropolitan 
area.  Were  Boston's  parks  again  to  be  infested  as  formerly;  were  the 
forests  in  the  Middlesex  Fells,  for  example,  to  be  defoliated,  a  wave 
of  remonstrance  would  arise  which  might  be  heard  halfway  across 
the  continent.  But  a  thousand  acres  of  forest  in  the  sparsely  popu- 
lated and  financially  poor  towns  30  to  50  miles  away  may  be  repeatedly 
defoliated  and  ultimately  destroyed  without  creating  more  than  a 
ripple  in  comparison.  And  this  latter  is  precisely  what  is  taking 
place  at  the  present  time.  It  will  be  necessary  to  wait  until  in  its 
slow  progress  the  gipsy  moth  invades  another  great  metropolitan 
area  before  popular  interest  will  be  aroused  to  an  extent  comparable 
to  that  existing  in  Massachusetts  a  few  years  ago. 

The  real  amelioration  so  noticeable  in  the  metropolitan  district,  and 
distinctly  in  evidence  everywhere,  is  due  to  at  least  four  main  causes: 
(1)  The  perfection  and  standardization  of  the  methods  for  artificial 
repression;  (2)  the  death  of  a  large  proportion  of  the  more  susceptible 
trees  or  their  removal  from  the  infested  woodlands;  (3)  the  importa- 
tion of  parasitic  and  predatory  insect  enemies;  and  (4)  the  develop- 
ment of  the  "wilt"  disease. 

As  it  is  intended  at  this  time  to  consider  the  gipsy  moth  strictly  as 
a  forest  insect  no  mention  need  be  made  of  the  methods  for  artificially 
suppressing  it.  On  account  of  their  expense  these  methods  can  not 
be  used  in  forests  other  than  those  which  it  is  desired  to  protect  for 
aesthetic  and  sentimental  reasons. 

RESULTS   OF   PARASITE    IMPORTATION. 

There  are  about  30  species  of  insect  enemies  of  the  gipsy  moth  which 
appear  to  be  of  importance  in  checking  its  increase  in  Europe  and 
Japan.  All  of  the  promising  species  have  been  imported  and  colo- 
nized under  more  or  less  satisfactory  conditions  in  America.  Not  all 
have  successfully  accommodated  themselves  to  their  new  environment. 
About  one-third  of  the  total  appear  to  have  done  so  and  to  be  steadily 
increasing  in  efficiency  in  accordance  with  their  powers  of  multipli- 
cation and  dispersion. 

It  was  hoped  that  more  of  them  would  acclimatize  themselves;  it 
was  feared  that  the  number  might  be  less.     On  the  whole,  the  results 


i  III    QIP81     MOTE     IB    \    i  0RE81    i.\>i  I   I  .  .*{ 

are  decidedl)  satisfying,  and  the  State  ol  Massachusetts  and  the 
United  States  Department  of  Agriculture  have  qo  cause  to  regrel 
having  undertaken  the  unexpected!)  formidable  task  of  parasite 
importation.  Within  a  territory  centering  a  little  to  the  uorthward 
of  Boston,  it  may  be  conservative^  9tated  thai  fulrj  50  per  cent  of 
the  eggs,  caterpillars,  or  pupa?  of  the  gipsy  moth,  in  the  ate, 

were  destroyed  by  imported  parasites  in  1912.  The  territory  over 
which  the  imported  insect  enemies  have  spread  is  uol  yel  verj  exten- 
sive, but  ii  is  extending  not  a  hi  \  from  year  to  year,  and  there  is  e\  ery 
reason  to  believe  thai  the  mortality  to  which  the  gipsj  moth  is 
already  subjected  in  this  central  portion  of  the  infested  area  will 
eventually  be  considerably  increased  throughout  it-  whole  extent, 
ae  additional  work  will  be  done  toward  assisting  in  the  dispersion 
of  certain  species,  and  it  may  be  thai  a  ne\t  attempl  will  be  made  to 
import  under  more  sal  isfactorj  conditions  certain  others  which  appear 
uol  to  have  established  themselves  as  the  result  of  earlier  attempts. 
Otherwise  the  work  of  parasite  importation  may  be  considered  as 
completed. 

THE    "WILT"    DISEASE    OF   THE    QEPS1     MOTH 

More  than  to  the  parasites,  more  than  to  the  perfection  of  the 
methods  of  artificial  suppression,  the  amelioration  in  conditions  is 
due  to  the  "will  "  disease.  This  is  a  malady  similar  to  or  suggestive 
of  the  flacherie  of  the  silkworm.  According  to  recent  investigations 
it  is  i\uv  to  parasitism  by  a  bacterium  which  has  been  described  under 
the  name  t>(  Qyrococeus  Hacddifex  by  its  discoverers,  Messrs.  Glaser 
and  Chapman,  working  under  the  direction  of  Dr.  W.  M.  Wheeler,  of 
the  Busse)  Institution.  While  it  is  uot  positively  proved  thai  this 
bacterium  is  the  cause  of  the  disease,  there  are  no  good  grounds  for 
doubting  and  many  for  believing  thai  it  is.  Confirmation  is  expected 
as  the  resull  of  further  cooperative  investigations  now  under  way  by 
the  Bureau  of  Entomology  and  the  Bussey  Institution. 

Although  we  know  very  little  of  the  bacterium,  we  know  much  <>f 
the  malady.  According  to  the  mosl  trustworthy  observers  it  first 
appeared  aboul  1903  or  1904  in  certain  of  the  worsl  infested  forests, 
and  t>\  1907,  when  the  present  writer  lir-t  became  associated  with  the 
gipsy-moth  work,  it  was  everywhere  in  evidence  throughout  the 
infested  area.  It  seemed  slight  ly  to  increase  in  the  year-  immediately 
following  and  to  have  reached  a  climax  aboul  1911.  At  the  present 
time,  fortunately,  there  is  nothing  to  indicate  that  it  is  at  all  likely 
to  become  much  if  any  le>»  effective  in  the  immediate  future. 

We  do  not  yet  know  how  the  caterpillars  originally  become  infected, 
hut  once  infected  there  is  hardly  room  for  doubting  thai  the  organ- 
ism itself  is  conveyed  from  one  generation  to  another  through  the 
Simple  infection  is  by  no  mean-  sufficient  to  cause  death.     On 


4  THE    GIPSY    MOTH    AS   A    FOREST    INSECT. 

the  contrary,  if  conditions  are  otherwise  favorable  an  infected  cater- 
pillar will  live,  complete  its  transformations,  and  (it  is  believed) 
transmit  the  germs  of  the  disease  directly  to  its  offspring.  Under 
these  circumstances  generation  could  follow  generation,  and  in  the 
course  of  time  the  race  of  gipsy  moths  might  gradually  be  purged  of 
the  disease,  so  that  eventually  only  a  few  individuals  would  carry  it. 

This  would  all  be  changed  were  the  infected  caterpillars  to  become 
weakened  through  any  other  cause.  Under  such  circumstances  an 
apparently  healthy  individual  will  sicken  and  die,  and  in  a  surpris- 
ingly short  time  the  entire  contents  of  its  body  will  be  resolved  into 
a  black  liquid  containing  countless  myriads  of  the  germs  of  disease 
where  before  there  were  but  few.  Death  is  particularly  likely  to 
ensue  upon  the  topmost  twig  of  the  tree,  and  the  disintegrated  bod}* 
of  the  victim,  breaking  of  its  own  weight,  permits  the  black  poison 
to  defile  the  foliage  below.  Another  caterpillar  feeding  upon  this 
foliage  contracts  the  disease  and,  provided  it  also  be  weakened 
through  any  other  cause,  it  quickly  dies,  and  the  process  is  repeated. 

It  is  very  evident  that  the  more  abundant  the  caterpillars  chance 
to  be  in  a  given  forest  the  greater  the  chance  that  the  disease  will  be 
thus  transmitted;  the  more  these  caterpillars  chance  to  be  weakened 
through  a  lack  of  suitable  food  the  more  likely  the}'  are  quickly  to 
succumb  and  transmit  the  malady  to  their  fellows.  It  thus  results 
that  when  a  forest  is  threatened  with  defoliation  by  infected  cater- 
pillars the  disease  becomes  epidemic  and  spreads  with  astounding 
rapidity. 

A  yet  more  important  cause  for  the  development  of  the  "wilt "  than 
partial  defoliation  is  to  be  found  in  unfavorable  food.  It  used  to  be 
easy  to  rear  caterpillars  in  the  laboratory  upon  lettuce,  for  example, 
when  they  were  free  from  the  taint  of  the  disease,  but  it  is  practically 
impossible  to  do  so  to-day,  if  American  eggs  are  used.  With  foreign 
eggs,  collected  from  a  locality  where  the  wilt  is  not  prevalent,  this 
did  not  prove  to  be  the  case  in  the  course  of  experiments  recently 
conducted  at  the  Gipsy  Moth  Parasite  Laboratory,  which  it  is  pro- 
posed to  repeat  the  present  year.  Nor  is  lettuce  an  exception  among 
foods.  The  same  may  be  said  of  practically  all  herbaceous  plants, 
and,  fortunately,  of  a  considerable  variety  of  trees  and  shrubs. 

Herein  lies  the  most  potent  cause  for  the  less  destructive  character 
of  the  gipsy  moth  in  recent  years,  according  to  the  opinion  of  the 
writer — an  opinion  which  it  is  expected  will  be  abundantly  confirmed 
in  the  course  of  the  coming  summer.  And  herein  lies  the  real  secret 
of  the  practical  resistance  of  certain  species  of  trees  to  gipsy-moth 
attack. 


Till:   UIPS1     Moiii     \-    \    PORES!     INSECT.  5 

\i;  1 11  li  I  M     I    riUZATION    01      i  ill  WILT "    I 

h  seems  necessarj  to  emphasize  the  foregoing  statement  that  the 
resistance  of  certain  species  of  trees  is  directly  due  to  1 1  m  ■  suscepti- 
bility of  caterpillars,  feeding  upon  the  foliage  of  these  trees,  t<>  death 
through  the  "wilt"  disease,  and  thus  incidentally  i<>  emphasize  1 1 1< • 
\cr\  greal  importance  of  the  disease  itself.  Since  this  disease  is 
believed  to  result  from  parasitism  l>\  a  specific  bacterium,  tin-  propo- 
sition of  increasing  its  efficiency  through  infecting  the  caterpillara 
artificiallj  with  cultures  of  th<v  bacterium  al  mice  suggests  itself. 

This  possibility  is  largely  precluded  if  equal  emphasis  be  laid  upon 
tin"  real  character  of  the  disease,  bo  far  as  we  are  able  to  (let ermine  it , 
either  through  intensive  study  of  the  organism  believed  to  be  respon- 
sible or  tlirough  observations  upon  its  activities  in  the  field. 

At  the  presenl  time  wherever  caterpillars  ;ire  to  be  found,  infected 
caterpillars  have  been  found  also  upon  everj  occasion  when  search 
for  them  has  been  made.     Furthermore,  even  though  the  infection 

were  proved   to  he  w  ind-horne.  as  has  heen  contended      and   there  is 

room  for  doubl  regarding  this  mosl  essentia]  fact  every  particle  of 
reliable  evidence  indicate-  that  slightly  infected  caterpillars  remain 
reasonably  healthy.  The  condition  of  the  caterpillars  upon  the  arti- 
ficially protected  trees  along  the  roadsides  in  localities  where  an  epi- 
demic o(  the  disease  prevails  in  the  main  body  of  the  forest  i-.  or 
ought  to  be,  sufficient  evidence  of  this.  Notwithstanding  thai  these 
caterpillars  are  forced  to  feed  upon  trees  which  have  heen  sprayed, 
and  notwithstanding  that  through  artificial  suppression  alone  are 
they  prevented  from  stripping  the  trees,  those  which  escape  death 
amid  the  various  dangers  by  which  they  are  artificially  encompassed 
remain  remarkably  healthy,  and  with  comparatively  rare  exceptions 
there  i>  an  increase  in  cumbers  of  the  fresh  egg  masses  each  tail  over 
the  number  which  escaped  the  creosote  brush  the  preceding  spring. 
Rather  elaborate  experiment--  have  heen  carried  on  in  thepa-t 
to  determine  whether  the  disease  could  he  practically  transmitted 
through  infected  food,  and  with  one  not  a  hie  exception  those  who  have 
conducted  such  experiments  have  concluded  that  artificial  utilization  of 
the  disease  in  this  manner  i-  impracticable.  If  the  writer  is  not  mis- 
taken ir  was  Dr.  Roland  Thaxter.  of  Harvard  University,  a  specialist 

of  high   Standing  upon    the   vegetable   parasites  of   insects,   who  was 

the  lirst  actually  to  experiment  along  this  line,  and  who  was  the  first 
to  he  convinced  of  it>  futility.  In  1908  Dr.  Herbert  Johnson,  work- 
ing for  the  State  of  Massachusetts  in  cooperation  with  Harvard 
University,  conducted  an  elaborate  series  of  field  experiments  to  test 
this  theory,  hut  with  no  more  promising  results. 

Further  investigation  and  experimentation  were  conducted  coop- 
eratively  by  the  State  of  Massachusetts  and   Harvard   University 


6  THE   GIPSY,  MOTH    AS   A   FOREST   INSECT. 

under  the  direction  of  Dr.  E.  A.  Murk  and  Dr.  Theobald  Smith. 
working  more  or  less  independently,  and  still  the  results  were  nega- 
tive1. The  present  writer,  in  connection  with  the  work  of  parasite 
importation,  conducted  experiments  of  a  similar  nature  but  with  the 
usual  outcome.  The  difficulty  in  every  case  was  due  to  the  fact 
that  it  was  impossible  to  secure  healthy  caterpillars  for  either  the 
experiment  or  its  check.  It  made  no  difference  whether  the  cater- 
pillars were  fed  with  the  infected  food  or  not,  large  numbers  would 
die  in  any  event,  and  there  seemed  to  be  no  noticeable  difference 
between  the  mortality  in  the  experiments  and  in  the  checks. 

It  remained  for  Mr.  William  Reiff,  at  one  time  a  laborator}-  assist- 
ant in  the  Bussey  Institution,  to  claim  success  where  others  had 
failed.  His  experiments  were,  in  their  essential  characters,  like  those 
of  his  predecessors.  He  fed  some  caterpillars  upon  an  unfavorable 
food,  and  they  contracted  the  disease  and  died,  exactly  as  had  resulted 
in' all  other  recent  attempts  to  rear  caterpillars  in  the  laboratory  from 
American  eggs.  When  the  sick  and  dead  individuals  were  placed 
upon  badly  infested  trees  in  the  field  a  mortality  was  noticed  among 
the  other  caterpillars  in  the  vicinity.  The  fact  was  cheerfully  ignored 
that  a  similar  mortality  might  be  observed  in  every  other  locality 
where  the  same  degree  of  infestation  prevailed,  and  no  attempt  was 
made  systematically  to  determine  exactly  what  happened  in  these 
other  places.  In  this  most  important  respect  the  experiments  con- 
ducted by  Mr.  Reiff  differed  from  those  conducted  by  Dr.  Johnson. 

Such  a  series  of  check  observations  has  been  made  the  past  sea- 
son, quite  incidentally,  hi  connection  with  the  field-observation  work 
fts  conducted  by  Mr.  A.  F.  Burgess  of  the  Bureau  of  Entomology. 
The  final  results  of  this  work  for  the  season  are  not  yet  available,  but 
the  writer,  who  has  personally  visited  the  majority  of  the  observation 
points,  of  which  perhaps  20  per  cent  chanced  to  be  in  the  immediate 
vicinity  of  disease  plantings  of  the  summer  before,  has  been  abso- 
lutely unable  to  distinguish  a  single  point  of  difference  between  the 
treated  and  the  untreated  localities.  In  every  badly  infested  locality 
complete  or  partial  defoliation  with  all  its  attendant  consequences 
resulted.  The  severity  of  the  injury  differed  notably  in  different 
localities,  as  was  to  be  expected,  but  if  extreme  instances  were  to  be 
cited  it  would  not  be  difficult  to  select  localities  where  no  disease  was 
planted  in  which  conditions  at  the  close  of  the  season  were  very 
much  better  than  in  others  where  plantings  had  been  made. 

Nor  is  there  anything  unusual  anywhere  in  the  infested  territory 
to  differentiate  conditions  this  fall  from  those  prevailing  a  year  or  two 
ago.  In  fact  it  is  the  writer's  personal  impression  that  rather  more 
pine  has  been  seriously  injured  in  1912  than  in  1911,  and  that  the  con- 
dition of  the  oak  is  worse  than  he  has  ever  seen  it  before.  In  short, 
nothing  whatever  that  is  tangible  has  yet  come  to  the  attention  of 


I  III.    i.ll'.M     \ln  I  II     VS    v    pokes  r   INSECT.  , 

anyone  associated  with  the  Bureau  of  Entomo  liich  can  be  used 

in  Biipporl  of  the  contention  that  the  disease  ma}  be  rendered  more 
efficient  through  artificial  dispersion.    The  extensive  experiments  con 
ducted  by  the  State  of  Massachusetts  in   1912,  in  pursuance  of   its 
policy   in  investigate  thoroughly  every  possible  method  of  ridding 
its  forests  of  the  gips)   moth,  would  appear  to  have  resulted  exactly 

as  did  the  earlier  and  less  elaborate  aeries  r lucted  \<\   Dr.  Johnson 

and  others 

\\iii.\i     CONTROl     01     I'll  I "    QIPS1     MOTH     \lti:n\u 

A  large  portion  of  the  past  two  years  has  been  spenl  by  the  writer 
abroad  in  studying  the  gips}  moth  in  its  original  habitat.  The 
objects  of  this  over-sea  work  were  several.  Ii  was  desired  more 
exactly  to  determine  the  part  played  by  the  parasites  in  holding 
the  gips)  moth  in  check  in  the  European  forests  and  to  ascertain 
whether  all  the  important  species  of  parasites  had  been  discovered. 
Were  promising  new  species  found,  attempts  wen  to  be  made  to 
ship  large  quantities  to  America  for  experimental  colonization. 
Above  all.  it  was  hoped  to  learn  whether  the  assumption  upon  which 
the  parasite  work  had  originally  been  undertaken  was  well  grounded; 
that  is,  whether  all  the  factors  responsible  for  the  natural  control 
of  the  gipsj  moth  in  the  European  forests  were  presenl  and  active 
in  America,  saving  only  the  parasites.  'The  results  of  this  work  are 
in  part  supplemented  and  in  part  confirmed  by  the  observations  of 
Mr.  L.  II  \Vuitl,le\ .  who  has  spenl  the  better  part  of  a  year  abroad, 
and  in  part  the\   are  pertinent   to  this  discussion. 

It  was  found  that  the  invasion  of  the  greater  pari  of  Europe  by 
the  gipsy  moth  some  three  to  se\en  years  ago  had  spent  its  force, 
and  that,  although  small  cumbers  of  the  inseel  might  be  found  in 
aearl)  every  oak  foresl  visited  in  Italj  and  Germany,  it  was  found 
abundant  in  verj  few.  It  was  difficult  to  ascertain  definitely  what 
had  occurred  to  check  this  general  invasion,  bul  it  is  certain  that  a 
disease  similar  in  all  its  external  manifestations  to  the  American 
"wilt"  (and  also  to  the  well-known  and  beneficent  ' '  w  ipfelkrank- 
heit  "  of  the  nun  moth1  had  prevailed  in  many  localities,  including 
some  in  Kussi;i.  Italy,  and  Germany.  It  seemed  to  have  heel)  epi- 
demic in  all  nf  the  localities  which  had  been  badly  infested  by  the 
gipsy  moth. 

It  was  also  evident  that  following  the  enormous  decrease  in  cum- 
bers brought  about  l>\  this  epidemic  there  was  nothing  like  the  phe- 
nomenal increase  of  the  straggling  remainder  so  frequently  observed 
in  America.  Instead,  when  an  innocuous  minimum  was  reached 
this  desirable  condition  was  maintained  for  an  indefinite  and  some- 
times for  a  protracted  period.     It  appeared  highly  probable     and  this 


8  T11K    GIPS1     MOTH    AS    A    FOBBST    INSECT. 

probability  was  supported  by  definite  confirmatory  evidence — that 
the  failure  of  the  moth  immediately  to  increase  was  due  as  much  as 
anything  to  the  parasites;  and  a  wholly  unexpected  and  phenomenal 
rate  of  parasitism  was  found  to  prevail  in  some  localities.  Inci- 
dentally several  species  of  parasites  until  then  unrecognized  as  impor- 
tant or  promising  were  found  and  large  numbers  were  shipped  to 
America. 

The  role  played  by  the  parasites,  however,  was  obviously  less 
important  than  had  been  assumed  when  the  work  of  parasite  impor- 
tation was  inaugurated.  Generally  speaking,  it  appeared  that  though 
the  increase  of  the  moth  was  prevented  or  retarded  through  para- 
sitism, it  was  principally  if  not  invariably  through  disease  that  an 
actual  outbreak  was  checked. 

This  was  borne  out  by  the  circumstances  associated  with  two  local 
outbreaks  in  southern  Italy:  One  in  Sicily,  in  the  extensive  cork- 
oak  forest  of  San  Pietro,  near  Caltagirone,  and  the  other  in  the 
communal  forest  of  the  town  of  Gioia  Tauro,  in  Calabria.  In  both 
of  these  localities,  and  particularly  in  the  latter,  the  parasites  were 
abundant  and  varied.  In  neither  were  they  able  to  prevent  the 
rapid  increase  of  the  moth,  much  less  to  bring  about  a  decrease. 
In  both  the  defoliation  of  a  large  portion  of  the  forest  was  absolutely 
complete,  and  in  neither  was  the  "wilt"  disease  operative. 

The  conditions  in  the  foresl  of  San  Pietro  were  the  more  interesting 
and  instructive  because  the  invasion  there  was  of  no  less  than  12 
years'  standing.  At  no  time,  according  to  the  statements  of  the 
local  authorities,  had  the  entire  forest  been  defoliated  at  once,  but 
the  invasion  would  sweep  back  and  forth  over  it,  so  that  the  trees 
were  defoliated  about  every  second  or  third  year. 

Here  in  this  Sicilian  forest  all  the  amazing  stories  told  of  the  gipsy 
moth  upon  the  occasion  of  its  historic  outbreak  in  Maiden  and  Med- 
ford  were  abundantly  substantiated.  There  were  no  streets  and 
very  few  houses,  but  there  were  a  few  gardens,  fields,  orchards,  and 
vineyards,  and  an  abundance  of  wild  plants,  shrubby  and  herbaceous. 
Of  them  all,  wild  and  cultivated,  hardly  a  dozen  species  were  immune 
from  attack.  There  were  places  where  at  times  the  ground  was 
black  with  the  caterpillars  as  they  came  out  of  the  forest,  which  no 
longer  afforded  them  either  food  or  protection,  and  invaded  the  fields 
and  open  spaces.  Here  the  combination  of  burning  sand  and  blazing 
sun  resulted  in  the  agonizing  death  of  myriads,  and  their  dead  bodies 
could  have  been  swept  up  by  the  bushel. 

Neither  in  1911  nor  in  1912  was  a  single  caterpillar  dying  of  the 
wilt  observed.  Parasites  were  abundant  each  year,  destroying 
approximately  90  per  cent,  which  was  far  from  sufficient  to  prevent 
increase.     Each   year   the   millions   which    died   of  starvation    and 


1  HE   <.li'M     MO  I  ii     18    \    l  ORES  i    I  N  3E(   I . 

exposure  dried    up   without    showing   traces*    oj    the    decomposition 
in\ ariabh  associated  «  n h  i he  ''will 

As  a  resuh  ,  in  the  worst  infested  port  ions  of  the  f oresl  there  w 
be  very  iVw  eggs,  but  the  caterpillars  would  always  be  remarka 
health}  the  next  Beason,  and  as  the  parasites  would  be  attracted  to 
the  inure  badrj   infested  parts  of  the  foresl  the  rate  of  increa  i   i 
where  would  be  Bimpl}  astounding, 

In  the  Calabrian  foresl  the  invasion  had  not  passed  beyond  its 
preliminary  stages  in  1911,  but  l>\  1912  it  had  reached  it-  mi 
mum.  Here  conditions  were  the  same,  pxcepl  thai  as  the  surround- 
ing fields  offered  better  protection  from  the  glaring  sun  the  cater- 
pillars coming oul  of  the  foresl  lived  longeranddid  more  damage  to 
the  crops.  The  trees  in  both  forests  were  absolutel}  stripped  of  foli 
whenever  there  were  sufficient  caterpillars  and   not  left,  as  they 

commonly  in    America,    where  the  disease  is  prevalent,  with  a 
sprinkling  of  partly  eaten  leaves.     All  kinds  seemed  to  suffer  alike. 
There  were  no  conifers  except    a  few  cypress    (related  to  and  with 
foliage  very  like  our  white  cedar    which  gre\s  along  an  agave  hedj 
bordering  the  Sicilian  forest.     These  were  stripped  as  bare  as  the  oaks. 

In  no  locality  other  than  these  two,  whether  European  or  Amei  i< 
has  the  writer  been  able  to  find  the  gipsy  ninth  unaccompanied  by 
disease.  Ii  is  the  prevalence  of  such  extraordinary  conditions  and 
their  similarity  to  those  w  tiicfa  prevailed  in  America  before  the  devel- 
opment of  the  disease  which  serve  to  convince  him  thai  the  present 
improved  conditions  are  so  largely  <lue  to  the  presence  of  the  "wilt  " 
disease. 

FOREST    CONDITIONS     \-     I   FA<   TOR    l\    CONTROL. 

It  i-  obvious,  even  to  the  casual    American  traveler,  that  in  a 
European  countries  applied  forestry  is  developed   to  an  unfamiliar 
extent.     The  forests  are  treated  with  an  intelligent  respecl  for  tl. 
requirements  and   a  careful  consideration  for  their  continued  well- 
being  rarely  approached  in  America.     It  maj  even  he -aid  that  th 
are  among  the  mosl  stable  of  European  institutions.     Nations  h. 
risen  and  fallen,  hut   policies  of  foresl   management  adopted  half  a 
thousand  year-  ago  are  used  as  a  working  basis  in  those  same  fores 
to-day. 

This  being  the  case,  it  logically  follow-  that  if  the  gipsy  moth  had 
ever  threatened   the   European  forests  to  anything  hke  the  ext< 
that  it  threatens  American  forests  to-dai  .  method-  of  forest  mana 
men!  would  have  been  evolved  which,  either  con-  or  una 

sciously,  would  have  taken  it-  destructive  tendencies  into  considera- 
tion.    After  having  studied  the  gipsy  moth  in  these  fore-'-  both  Mr. 
Worthley  and  the  writer  are  much  inclined  to  the  opinion  that  son 
thing  very  like  this  has  taken  place. 


10  IKK   GIPS1     MOTH    AS   A    FOREST* INSECT. 

To  a  large  extent  the  European,  and  particularly  the  German, 
forests  differ  radically  from  those  within  the  area  infested  by  the 
gipsy-' moth  in  America.  Oak,  so  common  as  a  coppice  growth  in 
America,  is  relatively  little  grown  in  Germany,  and  when  successfully 
grown*the  forest  bears  little  resemblance  to  the  typical  American 
coppice.  It  has  been  stated  repeatedly  that  oak  is  not  materially 
injured  by  the  gipsy  moth  in  Germany,  even  though  the  trees  are 
occasionally  stripped,  because  they  refoliate  and  seem  to  retain  a 
fail-  amount  of  vigor.  Notwithstanding  this  statemenl  they  are  fre- 
quently in  had  condition,  particularly  in  forests  which  more  nearly 
approximate  in  character  the  American  coppice.  For  example,  in  a 
large  tract  near  Neusala-<  )<\cv  many  oaks  were  dead  or  dying-  Various 
causes  were  adduced  for  their  death,  such  as  attack  by  a  species  of 
Agrilus,  attack  by  a  fungous  disease,  attack  by  a  leaf-roller.  Tortrix 
virid'niitii,  etc.,  and  tin1  circumstance  that  they  had  been  defoliated 
several  years  before  by  the  gipsy  moth  was  not  considered  as  respon- 
sihlc  for  their  condition.  It  is  significant,  and  suggestive  of  the 
existence  of  a  parallel,  that  following  defoliation  by  the  gipsy  moth 
•in  America  tin'  trees  frequently  refoliate.  hut  are  suhsoquently 
destroyed  by  a  species  of  Agrilus,  or  by  a  fungous  disease,  or  by 
something  else  than  simply  defoliation. 

Oak  in  Germany  is  apt  to  become  stag-headed  -that  is.  to  die  pre- 
maturely from  the  top;  and  it  also  happens  frequently  in  America 
that  when  trees  have  been  once  or  twice  defoliated  by  the  gipsy 
moth  and  then  protected  from  further  injury  they  arc  affected  in 
the  same  way.  In  America  we  have  been  able  to  determine  and 
define  the  cause  of  the  injury  through  a  comparison  of  conditions 
outside  and  inside  the  infested  territory,  but  in  Germany,  where  the 
entire  country  may  be  said  to  be  infested,  such  comparison  is  not 
so  easy. 

There  are  numerous  other  points  which  might  be  brought  forward 
in  support  of  the  contention  that  in  Europe  the  liability  of  certain 
types  of  forests  to  serious  injury  through  occasional  defoliation  by 
the  gipsy  moth  has  long  been  taken  into  account  and  that,  albeit 
unconsciously,  methods  of  forest  management  have  been  modeled 
accordingly.  -  Without  attempting  to  reason  out  the  whys  and 
wherefores  the  pioneer  foresters  were  content  to  recognize  the  simple 
fact  that  certain  types  of  forests  might  not  be  grown  under  certain 
conditions  or  at  all,  and  whether  this  were  due  to  the  character  of 
the  soil,  or  to  the  climate,  or  to  the  presence  of  an  insect  like  the 
gipsy  moth  matters  not. 

Similar  recognition  of  similar  drawbacks  to  the  cultivation  of  cer- 
tain types  of  forest  is  probably  what  we  must  come  to  in  America. 
It  stands  forth  as  the  main  result  of  the  European  observations  that 
in   the  European  forests   the  gipsy  moth  is  held   in  check  by  three 


I  ill     i.II'm     \nu  II     kS  A  ]  OR!  -  i.  11 

urir-  which  did   no!  exist   in  America  al   the  time  of   the  earlier 
and  mosl  alarming  in>  asions 

l     ["he  pa 
1.  The  dis  i 

I'll"-  chars*  tor  of  t  hi    fori 

The  parasites  are  promising  to  become  about  as  efficient  here  as 
in  the  European  forests,  and  it  musl  not  l>c  forgotten  that  m>  more 
has  been  claimed  for  them  than  that  thej  would  render  the  gips) 
moth  as  innocuous  here  as  in  it--  original  habitat. 

The  disease,  t<>".  is  about  as  efficient  here  as  it  is  abroad. 

Perhaps  it  is  not  too  much,  then,  to  demand  that  forest  conditions 
in  America  be  made  to  conform  a  little  more  nearh  to  those  of  the 
countries  in  winch  the  gipsj   moth  is  native,  particularly   to  those  of 

1      •  main  . 

Tli i-  does  no1  by  any  means  imprj  the  adoption  of  European  foresl 
methods  en  masse,  but  rather  that  the  forests  be  given  a  little  better 
attention  and  that  provision  be  made  f< >r  the  actual  or  inevitable 
invasion  by  the  urip^.\  ninth  through  the  elimination  <>f  those  tn 
most  likely  t<>  be  injured  and  their  replacement  by  others  less  3us 
ceptible  and  not  infrequently  mine  valuable.  As  a  matter  of  fact 
this  removal  and  replacement  is  taking  place  automatically  in  the 
territory  thai  has  been  longest  infested,  bul  the  natural  process  i- 
Tim  often  accompanied  by  unnecessary  destruction  of  other  trees  and 
unnecessary  pecuniary  loss. 

RELATIVE     SUSCEPTIBILITl      •>!       AMERICAN      FORES!      iREES      TO     QIPSY 

MOTH     \  I  r  \i  K 

As  has  been  stated,  at  the  time  when  the  firsl  real  invasion  by  the 
gipsy  moth  in  the  United  States  was  at  it-  height  it  was  believed 
that  scarcely  any  forest,  shade,  or  fruit  tree  was  resistant  to  it- 
attack.  And.  as  has  been  explained,  the  appearance  of  disease,  fol- 
lowing a  period  of  uninterrupted  increase  of  the  moth,  was  accom- 
panied by  a  change  in  tln>  respect.  That  this  change  was  \rvy 
largely  due  to  the  disease  is  further  indicated  by  the  similarity  of 
the  conditions  prevailing  in  certain  Sicilian  and  (alahrian  for 
to-day  to  those  prevailing  in  Medford  and  Maiden  in  1889 

The  relative  susceptibility  of  certain  tree-,  to  injury  and  the  relative 
immunity  of  others  is  therefore  very  largely  due  to,  and  dependei  t 
upon,  the  presence  of  disease.  But  since  i  he  disease  is  everywhere  and 
bids  fair  to  remain  until  possibly  the  gipsy  moth  i-  freed  of  its  taint 
through  a  long  -erics  of  generations  passed  under  ideally  healthy  and 
favorable  surroundings,  there  seems  t.>  be  no  reason  why  the  neces- 
sary dependence  should  not  he  placed  in  it  without  fear  of  serious 
consequences. 


12  THE    GIPSY    MOTH    AS   A    FOREST    INSECT. 

At  the  same  time  the  writer  is  averse  to  committing  himself  to  the 
extent  of  stating  positively  that  the  methods  of  forest  management 
to  be  suggested  further  on  will  invariably  prove  successful.  Ho 
wishes  to  emphasize  the  truth  as  he  sees  it.  thai  the  relative  freedom 
from  injury  of  certain  type-  of  forest  is  dependent  upon  the  "wilt," 
and  that  their  continued  well-being  will  largely  depend  upon  the 
persistence  of  this  malady. 

lie  wishes  further  to  emphasize  his  belief  that  an  increase  in  the 
efficiency  of  the  parasites  will  add  to  the  variety  of  the  forests  which 
may  he  cultivated  to  advantage,  but  that  it  will  not  result  in  pro- 
tection to  all  the  types  which  at  present  are  to  he  found  in  the  area 
of  infestation.  The  suggestion  that  experiments  hi'  conducted  to 
determine  the  practicability  of  the  "reserve-tree"  method  of  culti- 
vating oak  is  made  only  on  the  assumption  that  the  parasites  will 
eventually  render  more  efficient  aid  than  at  present  and  in  a  le>s 
limited  portion  of  the  infested  territory. 

In  1908  Mr.  A.  II.  Kirkland,  in  his  third  annual  report  as  superin- 
tendent of  work  against  the  gipsy  and  brown-tail  moths,  first  called 
attention  to  the  apparent  resistance  of  white  pine  unless  associated 
with  hardwood  trees.  A  year  later  Mr.  L.  II.  "Wort  blew  his  acting 
successor,  published  in  the  next  report  the  results  of  experiments 
winch  showed  that  this  was  indeed  the  case,  and  that  pure  stands  of 
pine  might  he  protected  at  a  very  reasonable  expense. 

Partly  in  pursuance  of  this  idea,  and  partly  independently,  Messrs. 
1).  M.  Rogers  and  A.  F.  Burgess,  of  the  Bureau  of  Entomology,  after 
observing  the  activities  of  the  moth  in  the  field,  concluded  that  in 
addition  to  pine  most  of  the  other  conifers,  and  certain  hardwood  trees 
as  well,  might  he  considered  as  sufficiently  resistant  to  escape  serious 
injury.  Ash,  hickory,  and  maple  were  mentioned,  and  recommenda- 
tion was  made  jointly  in  Bulletin  87  of  this  bureau  that  such  trees 
he  planted  in  place  of  those  which  were  destroyed. 

These  recommendations,  made  in  1910,  were  succeeded  by  further 
observations  by  employees  of  the  Bureau  of  Entomology  and  the 
Massachusetts  State  forester's  office  with  the  result  that  by  the  fall 
of  1911  several  important  additions  had  been  made  to  the  list. 

Exact  information,  however,  was  lacking,  and  because  of  the 
obvious  need  for  it  a  series  of  investigations  was  inaugurated  under 
the  direction  of  Mr.  Burgess.  These  were  so  planned  as  to  demon- 
strate not  only  what  happened  when  caterpillars  were  confined  to 
certain  soils  of  food  indoors,  hut  exactly  what  happened  following 
invasion  of  different  types  of  forest  out  of  doors.  More  than  250 
observation  points  were  selected,  representative  of  every  type  of  pure 
and  mixed  forest  which  could  he  easily  located  within  the  infested 
area.      In  addition  to  pure  stands  of  pine,  oak.  and  birch,  for  example. 


I  III     0IP8>     Mmi  ii     \-    \    i  0R1  BT  INSECT.  1  ■ "• 

mixed  Btands  of  oak  and  pine,  birch  and  pine,  oak  and  birch,  etc., 
w  ere  Belectod. 

\  circle  hhi  feel  in  diameter  was  laid  off  around  h  central  tree  in 
the  midst  of  the  foresl  selected,  every  tree  included  was  numbered, 
and  notes  were  made  covering  its  species,  size,  general  condition,  and 
degree  of  infestation.  The  total  number  <>f  egg  masses  t"  be  found 
within  the  circle  was  recorded,  and  their  increase  or  decrease  from 
year  to  year,  together  with  the  actual  extent  of  injury  resulting  in 
ee  of  bad  infestation,  was  to  be  taken  as  the  measure  of  resistance 
offered  bj  thai  particular  type  of  forest. 

Although  tin-  work  is  n<>!  yel  complete,  the  results  already  Becured 
are  too  pertinent  and  valuable  to  be  reserved  until  its  conclusion. 

Rather  for  convenience  than  because  the  proposed  classification 
i-  altogether  natural  the  inure  common  shade  and  foresl  trees  of 
New  England  ma\  be  separated  into  groups  in  accordance  with  their 
wsceptibilit)   to  injury. 

The  Bret  of  these  groups  consists  of  those  trees  upon  w  bich  the  ninth 
following  its  establishment  norma  II  \  increases  to  the  poinl  of  complete 
or  nearly  complete  defoliation.  After  the  first  defoliation  the  moth's 
numbers  may  be  very  greatly  reduced  or  the}  may  remain  practically 
the  same.  In  the  one  case  one  or  more  years  may  elapse  before  de- 
foliation is  repeated.  In  the  other,  the  forest  ma\  be  defoliated  for 
several  year-  in  succession.  In  either  case  the  trees  are  likely  to  be 
severely  injured  and  to  die. 

This  group,  bo  far  as  known,  is  composed  exclusively  of  the  various 
oaks,  with  the  possible  but  not  proved  exception  of  the  shrubby 
Bpecies  These  may  be  considered  as  representing  the  most  favored 
food  plants  of  the  gipsy  moth. 

The  second  group  consists  of  those  tree-  which  appear  to  be  espe- 
cially favorable  to  the  increase  of  the  moth  immediately  following 
its  establishment.  Almost  always,  however,  at  about  the  time  when 
defoliation  would  result  were  the  colon]  to  remain  healthy,  it  receives 
a  set  hack.  The  trees  are  rareh  completely  s<  ripped,  and  though  they 
may  be  from  one-half  to  three-fourths  defoliated  for  several  successive 
years,  death  rarely  follow-. 

The  most  notable  representatives  of  this  group  are  several  of  the 
tree  willows  and  the  gray  birch.  It  i-  possible  thai  some  other  trees 
will  eventually  he  included;  hut  none  other  30  commonly  encoun- 
tered in  the  territory  at  pre-ent  infested  by  the  gipsj  moth  will 
Compare  directly  with  birch  or  willow  These,  through  the  protec- 
tion which  they  afford  to  incipient  colonic-  of  the  gipsy  moth,  act 
a-  incubators  or  breeders. 

In   the   third   group   are   to   he   placed    t  ho-e   trees   upon   which   the 

gipsj  moth  rarely  increases  to  the  extent  usual  upon  gray  birch  01 
willow.     Upon  Borne  it  will  increase  until  a  fair  degree  of  infestation 


14  THE   GIPSY    .MOTH    AS   A    FOREST    [NSECT. 

results,  l)iit  rarely  to  the  point  of  noticeable  defoliation.  Upon  others 
it  will  barely  hold  its  own,  and  upon  a  few  there  wiJ]  be  a  decrease  in 
abundance  following  any  considerable  degree  of  accidental  infesta- 
tion. These  trees  are  what  is  here  called  resistant,  and  nearly  all 
of  them  are  practically  that,  so  long  as  the  "wilt  "  remains  as  efficient 
as  it  is  at  present. 

In  this  group  are  to  be  placed  the  pines;  the  spruces; in  all  prob- 
ability fir;  hemlock,  with  scarcely  a  doubt,  though  it  is  notably  more 
favorable  than  pine  as  a  food  plant:  the  junipers  and  cedars:  doubt- 
fully larch:  some,  but  perhaps  not  all,  of  the  poplars;  chestnut: 
probably  beech:  yellow  birch,  black  birch,  and  probably  paper  birch: 
apparently  all  the  species  of  hickory;  butternut:  sycamore:  Ameri- 
can elm,  and  probably  the  other  species  of  elm:  apparently  hack- 
berry;  sassafras:  catalpa;  the  various  species  of  ash:  black  locust 
and  honey  locust:  black  cherry  and  bird  cherry:  probably  mountain 
ash:  all  the  indigenous  and  probably  the  European  species  of  maple, 
although  the  Norway  maple  is  more  liable  to  attack  than  others: 
boxelder;  tupelo;  horse-chestnut;  ailanthus;  tulip  tree,  and  undoubt- 
edly many  other  of  the  less  commonly  planted  shade  and  ornamental 
trees. 

A  few  of  the  more  common  trees  have  not  yet  been  definitely 
placed,  notably  basswood  or  linden,  ironwood.  and  hop  hornbeam. 

RELATIVE    SUSCEPTIBILITY    OF    MIXED    FORESTS. 

It  would  thus  appear  that  in  a  territory  in  which  both  disease  and 
parasites,  or  disease  alone,  is  prevalent  the  gipsy  moth  becomes 
peculiarly  an  enemy  of  oak,  and  this  is  true  in  so  far  as  pure  stands 
of  trees  are  concerned,  or  of  isolated  trees.  It  is  not  so  true  of  mixed 
stands,  however,  as  was  pointed  out  by  Mr.  Kirkland  and  by  Mr. 
Worthley  in  respect  to  pine  mingled  with  hardwood,  and  these  mixed 
stands  may  generally  be  considered  just  a  little  more  resistant  than 
would  be  a  pure  stand  of  the  least  resistant  tree  and  considerably 
less  resistant  than  a  pure  stand  of  the  most  resistant  tree  which  goes 
to  make  up  any  considerable  portion  of  the  mixture.  Thus  a  pine 
and  oak  forest  is  slightly  less  liable  to  injury  than  a  pure  stand  of 
oak  and  much  more  liable  than  a  pure  stand  of  pine.  The  same 
might  be  said  of  an  oak  and  hickory  mixture  or  one  of  oak  and 
chestnut.  The  reason  is  that  the  caterpillars,  increasing  uninterrupt- 
edly upon  oak.  will  finally  be  forced  to  leave  it  and  will  strip  other 
trees  upon  which  they  would  not  increase  to  anything  like  a  similar 
extent  if  they  were  forced  to  feed  upon  them  for  generation  after 
generation.  They  do  not  always  do  this,  it  is  true,  but  they  do  it 
very  often,  particularly  when  the  oak  is  abundant  and  scattered 
evenly  throughout    the  forest. 


I  ill.   GDPB1     HOTS     18    \    i  0BE8T    tv-M    i .  1  B 

Since  hemlock  i-  better  liked  Mian  pine  l>\  tin-  caterpillars,  a  mixed 
growth  of  oak  ami  hemlock  is  much  more  likely  in  he  destroyed  com- 
pletely than  :i  mixed  growth  «>t'  oak  ami  pine:  ami  since  graj  birch 
i-  ii< » i  -i.  favorable  a  food  plant  as  oak,  a  birch  and  pine  mixture  ie 

not   nearly  ><>  likely   In  Buffer  a-  a    mixed   -land  of  nak  ami   pine. 

Apparent!}  no  fear  oeed  he  felt  as  to  the  safety  of  anj  mixture 
whatever  of  which  all  the  component  parts  could  he  considered  as 
resistant  it"  they  were  Btanding  in  pure  growth.  As  •<>  the  greater 
resistance  of  an  oak  tree  when  Btanding  Burrounded  l>>  chestnut  ami 
hickory,  a-  compared  with  another  of  the  same  Bpecies  and  vigor 
surrounded  by  oak.  there  is  room  for  Further  investigation.  It  can 
only  he  -aid  that  the  protection  thus  afforded  i<>  oak  through  being 
associated  with  other  tree-  i-  not  particularly  Btriking. 

RELATION    or    UNDERBRUSB    TO    THE    FOREST. 

li  i-  interesting,  in  connection  with  the  relative  resistance  of  forest 

trees,  to  note  that   the  aprouts  and,  t>>  a  Ie--  extent,  the  seedlingB,  are 

not  bo  liable  to  injury  a-  are  Larger  tree-  of  the  same  Bpecies.  This 
i-  tine  even  of  pine,  mile—  the  writer  ha-  misinterpreted  his  field 
observations. 

Il  i-  al-o  true  thai  for  the  nio-t  part  tin-  common  species  ol  -liruh- 
to  he  found  growing  a-  u.nderhru-h  in  a  forest  air  unfavorable  BS 
food  for  tin-  gipsy   moth      that    i-   to  -ay.   they   ma\    he  classed    with 

the  resistant  species  of  trees.  It  i-  certainly  logical  and.  to  that 
extent,  reasonable  to  suppose  that  underbrush  will  he  found  to  play 
quite  an  important  part  in  the  protection  of  the  forest.  Caterpillars 
falling  from  tree-  in  a  pure  -land  of  oak  devoid  of  underbrush  will 
find  their  way  back  to  oak  and  be  little  tin-  worse  for  the  adventure. 
Caterpillars  falling  in  a  similar  manner  in  a  forest  full  of  underbrush 
will  not  find  their  way  hack  bo  readily,  and  the  eating  of  strange 
food  for  h  time  will  render  them  Ie—  resistant  to  disease,  more  likely 
to  die.  and  therein  more  likely  to  transmit  the  germs  of  disease  to 
their  fellows. 

It  is  a  subject  well  worthy  of  further  study  ami  experimentation 
and  one  to  which  it  is  hoped  to  devote  considerable  attention  in  the 
course  of  the  coming  year,  the  mote  -o  since  it  ha-  special  bearing 
upon  the  suggestion  that  oak  might  possibly  he  protected  by  adopt- 
ing the  method  ot  cutting  so  a-  to  leave  reserve  trees. 

BE]   \TIY1.    RESISTANCE    OF    DIFFERENT    TREES    OF    tut     SAME    SPECIES. 

It  would  appear  from  numerou-  observations  that  certain  indi- 
vidual trees  (of  red  oak.  for  example)  are  much  better  able  to  with- 
stand the  attack  ot  the  irip^y  moth  than  others  of  the  same  species 
growing  in  the  same  wood  lot.  These  tree-,  although  they  are  sub- 
jected to  the  same  degree  of  defoliation,  will  live  when  all  around 


16  THE    GIPSY    MOTH    AS    A    FOREST    INSECT. 

them  die  and  even  take  on  new  life  and  vigor  through  coming  into  a 
larger  share  of  light  and  space.     It  is  yet  to  be  determined  whether 

these  trees  are  more  resistant  or  whether,  through  standing  in  some 
favored  pockets  of  richer  soil,  they  simply  survive  through  the  pos- 
session of  a  more  vigorous  constitution. 

It  is  undoubtedly  true  that  vigorous,  rapidly  growing  trees  are 
more  resistant  than  other  trees  of  the  same  species  less  vigorous 
and  less  rapidly  growing.  Thus  oak  trees  around  the  border  of  an 
infested  wood  lot,  with  more  room  to  expand  their  roots  and  branches, 
not  infrequently  live  when  all  or  nearly  all  the  more  crowded  indi- 
viduals in  the  depths  of  the  wood  lot  die.  It  is  also  true  that  isolated 
trees  withstand  a  greater  degree  of  defoliation  than  those  in  dense 
growth. 

Advantage  seems  to  have  been  taken  of  this  principle  in  the  method 
of  growing  oak  formerly  in  vogue  in  Germany,  for,  if  the  writer  is 
correctly  informed,  the  finest  and  largest  oaks  in  the  Empire  are 
grown  more  or  less  isolated  and  parked.  When  the  relative  immu- 
nity of  young  sprouts  is  also  considered,  a  very  logical  reason  is 
suggested  for  the  fact  that  the  method  of  leaving  reserve  trees, 
scattered  over  a  territory  devoted  principally  to  the  growth  of  sprouts 
or  coppice,  finds  so  much  favor  in  certain  parts  of  Europe.  The-e 
reserve  trees  are  left  practically  isolated  in  the  forests  which  have 
come  to  the  writer's  personal  attention,  and  the  sprouts,  for  which 
there  is  a  read}7  market,  unfortunately  lacking  in  America,  are  cut 
at  quite  frequent  intervals. 

SUGGESTIONS  FOR  THE  MANAGEMENT  OF  FOREST  LANDS   WITH    REFER- 
ENCE  TO   THE    GIPSY    MOTH. 

It  is  by  no  means  to  be  understood  that  because  of  the  gipsy  moth 
all  the  oak  in  this  country  is  foredoomed  to  destruction,  but  atten- 
tion must  be  called  to  what  is  undoubtedly  the  truth,  that  unless 
parasitism  or  disease,  or  something  else  not  at  present  recognized  as  a 
variable  factor  in  the  natural  control  of  this  pest,  develops  to  an 
extent  unknown  in  either  America  or  Europe,  pure  and  mixed  stands 
of  oak  will  be  seriously  injured.  Not  only  is  the  oak  itself  liable  to 
injury,  but  also  other  trees  mixed  with  it. 

It  is  yet  too  soon  to  state  definitely  whether,  in  localities  where 
there  is  no  oak,  other  trees  may  not  act  as  breeders  of  the  moths  to 
an  equally  disastrous  extent.  For  instance,  the  paper  birch  in  the 
north  woods  may  so  foster  it  as  to  bring  about  the  defoliation  of 
adjacent  spruce.  The  results  of  field-observation  work  in  occasional 
bits  of  forest  in  the  infested  territory  when1  spruce  and  birch  occur 
are  not  in  themselves  sufficient  to  settle  the  question,  because  condi- 
tions so  far  from  the  large  body  of  boreal  forest  can  not  be  considered 


i  in-:  i.ll-s\    Mm  ii    \>    \    i  (mm  ST  INBBOT.  17 

as  rralh  typical.  s.>  far  as  they  go,  however,  they  indicate  thai  the 
gipsy  moth  is  not  to  l)<"  feared  outside  the  range  of  the  oak  dr  in 
forests  inside  that  range  provided  the  oak,  and  possibly  one  or  two 
other  species  of  unimportant  trees,  be  eliminated. 

There  are,  therefore,  two  phases  of  the  complex  problem  of  gipsy- 
moth  control  in  forests  which  must  be  considered.     Firet,  how  best 

to   eliminate    the    oak    and    -ecure    it-    replacement    by    other   ami,    if 

possible,  more  valuable  trees;  and,  second,  how  besl  to  proteel  the 

oak  from  aerious  injury  in  localities  where  little  else  can  he  grown  to 

adi  antage. 

In  a  large  portion  of  the  area  at  present  infested  by  the  lt i j > - > 
moth  the  solution  is  almost  absurdly  simple.  This  is  the  natural  home 
of  the  white  pine,  one  of  the  most  valuable  timber  trees  to  be  found 
in  the  whole  Temperate  Zone.     In  a  way  the  oak  is  an  interloper. 

Over  a  large  part  of  New  England  the  white  pine  was  once  preeminent . 

and  it  would  become  so  again  were  the  country   to  be  deserted  by 

civilized  man.  The  pine  reproduces  freely,  if  given  half  a  chance, 
hut  there  are  thousands  of  acres  in  the  aggregate  in  which  a  natural 
reproduction  of  pine  is  being  retarded,  destroyed  even,  through  the 
mare  circumstance  that  the  oak  chanced  to  secure  a  running  start, 
by  sprouting,  when  the  Land  was  last  cut  over.  The  German  forester 
who  would  permit  such  conditions  to  prevail  would  be  considered 
hopelessly,  even  criminally  insane.  Under  such  circumstances  oak 
is  to  be  considered  a-  a  weed,  and  the  advent  of  the  L'ip^y  moth  as  a 
blessing  when,  a--  sometime--  happens,  it  takes  the  oak  and  leaves  the 
pine.     If  it  would  always  do  jusl  that  and  nothing  more  it-  progress 

mighl  be  watched  with  a  certain  degree  of  complacency.      But  it  does 

not  always  stop  at  that  and,  what  i>  worse,  injudicious  cutting  not 
infrequently  results  in  greater  damage  than  would  be  done  by  the 

gipsy  mot  h  it-elf.  The  larger  pines  are  apt  to  be  cut  or  broken  down, 
and  the  -mailer  one-,  unable  to  compete  with  the  rapidly  growing 
oak  sprout-,  are  quickly  in  no  better  condition  than  before. 

The  natural  program,  therefore,  in  every  pine  and  oak  mixture, 
i-  so  to  eliminate  the  oak  a-  to  afford  the  pine  a  better  opportunity 
to  take  possession  of  the  ground.  How  thi-  may  he-t  be  accom- 
plished depends  entirely  upon  the  individual  characteristics  of  any 
particular  wood  lot.  And.  furthermore,  it  i-  strictly  a  problem  in 
applied  forestry  and  one  for  the  forester,  not  for  the  entomologist, 
to  solve. 

In  a  great  many  localities  where  the  white  pine  doe-  not  grow 
naturally,  or  in  winch  it  has  been  destroyed  through  injudicious  cut- 
ting and  extensive  forest  tire-,  there  is  to  be  found  a  stand  of  oak 
mingled  with  other  hardwoods.  In  these  forests  tin-  solution  is  not 
reached  quite  so  easily  or  -o  satisfactorily.     Chestnut   (saving  only 


18  THE    GIPSY    MOTH    AS   A    FOREST    INSECT. 

for  the  possible  injury  by  the  blight),  hickory,  paper  birch,  sugar 
maple,  and  ash  all  find  conditions  greatly  to  their  liking  in  one  or 
another  part  of  New  England,  and  all  are  desirable  substitutes  for 
oak.  There  are  certainly  some,  and  probably  numerous  localities  in 
which,  through  nothing  more  than  the  exercise  of  a  little  care  and 
intelligent  management,  the  oak  may  be  removed  and  its  natural 
replacement  by  these  other  hardwoods  may  be  secured  with  a  mini- 
mum of  expense. 

It  is  in  the  pure  stands  of  oak,  or  in  those  of  oak  mingled  with  much 
less  valuable  trees,  all  too  frequently  to  be  found  throughout  the 
infested  area,  that  the  problem  becomes  acute.  Here  the  land  must 
be  allowed  practically  to  go  to  waste,  or  planting  must  be  resorted  to, 
or  else  some  attempt  must  be  made  to  maintain  a  growth  of  oak. 
The  most  simple  method  would  seem  to  be  the  leaving  of  reserve 
trees.  The  chances  at  present  are  that  this  may  not  work  very  well, 
but  unless  the  relief  which  we  have  every  reason  to  expect  through  the 
further  development  of  the  parasites  be  denied  us,  there  is  a  chance 
that  in  the  near  future  it  will  prove  to  be  a  fairly  satisfactory,  cheap, 
and  eventually  remunerative  alternative  to  permitting  the  forests  to 
be  entirely  destroyed.  It  must  not  be  forgotten  that  when  the  oaks 
are  left  to  die  from  the  gipsy-moth  attack  they  very  rarely  sprout, 
and  a  pure  oak  stand  is  apt  to  degenerate  into  a  thicket  of  gray  birch 
or  something  even  less  intrinsically  valuable.  If  the  oak  be  thinned 
in  advance  of  the  gipsy-moth  invasion  the  sprouts  will  be  resistant 
for  a  period  of  years  at  least,  perhaps  until  the  parasites  become  so 
efficient  that  they  wall  protect  the  stand  of  reserve  trees.  It  is  even 
possible,  if  the  thinning  be  done  far  enough  in  advance  of  the  inva- 
sion, that  the  reserve  trees  will  have  increased  sufficiently  in  vigor 
to  resist  the  attack  of  the  moth  until  the  parasites  shall  have  multi- 
plied sufficiently  to  hold  it  in  check. 

All  these  suggestions  are  to  be  treated  as  such  and  as  nothing 
more.  The  author  is  no  forester  and  can  not  pretend  to  recommend, 
but  only  to  suggest.  He  has  had  the  advantage,  however,  of  four 
years'  study  of  the  insects  injurious  to  American  forests  under  the 
direction  of  the  foremost  forest  entomologist  in  America,  and  through 
subsequent  study  of  the  gipsy  moth  in  America  and  abroad  has 
reached  certain  pretty  definite  conclusions.  The  gipsy  moth  is 
distinctly  a  menace  to  our  forests,  but  it  is  really  no  more  to  be 
feared  than  any  one  of  several  forest  insects  native  to  tins  country. 
If  the  situation  be  rightly  viewed,  and  a  serious  attempt  be  made 
to  cope  with  it,  it  is  certain  that  the  results  will  redound  not  only 
to  the  benefit  of  the  forests  in  general  but  to  that  of  the  country 
at  large. 


I  ill    QIP81     \i"i  ii     IB  A  1  OR]  BT  INSECT,  I '» 

1111:    i\i\iim\m      1:1  .i,H   ii.-i  MIA  i  -    01      Mil      Mil    \TH>\ 

The  immediate  requirements  of  the  situation  are  thai  the  work 
be  conducted  in  a  hearts  spirit  of  cooperation  among  all  concerned. 
For  tin'  purpose  of  solving  t  li<'  problems  associated  with  the  elimina- 
tion of  oak  and  its  replacement  by  other  and,  if  possible,  more 
valuable  trees  the  Bureau  of  Entomology  has  allied  itself  with  the 
United  Stales  Forest  Service  and  hopes  also  to  continue  in  hearty 
accord  with  the  various  State  foresters  most  immediately  concerned. 
The  further  investigation  of  the  "wilt"  disease  will  l>e  conducted 
l>\  the  Bureau  of  Entomology  and  the  Bussej  Institution  working 
together.  Additional  information  concerning  the  relative  resist- 
ance of  various  t ices  standing  singly,  or  in  pure  or  mixed  growth, 
will  be  compiled  by  the  Bureau  of  Entomology,  which  will  also 
concern  itself  to  discover  exactly  whal  progress  is  being  made  by 
thi>  imported  parasites  and  predatory  enemies.  These  lines  of 
investigation,  observation,  and  research  are  all  being  directed  with 
one  single  end  in  view,  hov  besl  to  protecl  the  forest. 

Of  greal  importance,  also,  is  the  work  intended  to  restrict  the 
spread  of  the  gipsy  moth  beyond  the  boundaries  of  New  England. 
A  certain  amount  of  natural  spread  can  not  l>e  prevented,  especially 
through  uiml.  but  it  U  hoped  entirely  to  eliminate  the  danger  of 
an  immensely  more  rapid  spread  through  artificial  channels,  upon 
Qursery  Btock,  forest  products,  etc.,  shipped  from  infested  to  oonin- 
fested  territory.  It  is  also  hoped  considerably  to  retard  the  slow 
and  inevitable  natural  dispersion,  even  though  it  is  impossible 
entirely  to  prevent  it. 

The  natural  progression  of  tlie  moth  to  the  westward,  which  is 
the  most  to  be  feared  and  also  the  easiest  to  retard,  will  be  more 
effectively  controlled  if  the  woodland  colonies  along  the  western 
frontier,  and  for  that  matter  over  the  whole  infested  area,  are  sup- 
pressed. It  is  from  these  that  the  wind  spread  largely  comes  about. 
The  longer  they  can  be  kept  down,  the  less  the  likelihood  of  their 

becoming  a  source  of  infestation  to  the  country  beyond. 

Especially  along  the  frontier  the  colonic-,  .ire  at  first  feu  ami 
scattered,  and  while  everything  within  reason  will  be  done  toward 

their  suppression,  there  is  believed   to  be  justification  for  asking  the 

active  cooperation  of  foresl  owner--  directly  interested.     If  through 
a  modification  in  their  methods  of  handling  their  property  they  can 

save    themselves    from    what    would    now    appeal-   in    many    in-~t.ii 
to   be  certain   loss;   if   they   can   at    the  same   time   put    their  fort 
in  such  condition  a-  not  only  to  protecl  them  in  the  future  but  also 
to    render    them    more    intrinsically    valuable;  and.    finally,    if    they 
can  render  a  not   inconsiderable  public  service  through  helping  to 


20  THE   GIPSY    MOTH   AS   A   FOREST   INSECT. 

retard  the  progress  of  the  moth  into  territory  not  as  yet  infested, 
the  request  for  such  cooperation  would  appear  to  be  well  justified. 

This  project,  to  bring  good  out  of  the  evil  that  has  resulted  through 
the  establishment  of  the  gipsy  moth,  by  combating  it  through 
methods  which  would  make  American  forests  more  valuable  than 
they  have  ever  been  before,  is  no  mere  vision.  Evidence  enough 
of  its  practicability  in  the  case  of  the  mixed  stands  of  oak  and  pine 
already  referred  to  is  easily  found  and  sufficiently  convincing. 
That  other  types  of  natural  forests  may  be  handled  so  as  to  make 
the  outcome  advantageous  to  the  forest  owner  as  well  as  to  the 
whole  country,  it  is  only  reasonable  to  expect. 

The  Forest  Service  and  the  Bureau  of  Entomology  will  attempt 
to  do  their  share  of  the  work,  through  cooperative  study  of  the 
technical  aspects  of  the  problem.  Experimental  and  demonstrative 
work  must  precede  definite  recommendation,  and  in  this  the  aid  and 
assistance  of  the  forest  owners  themselves  must  be  secured.  If  a 
spirit  of  hearty  cooperation  can  be  established  and  maintained  it 
would  seem  as  though  the  problem  would  all  but  solve  itself. 

Approved: 

James  Wilson, 

Secretary  of  Agriculture. 
Washington,  D.  C,  November  J,  1912. 


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